- #1

Ras9

- 15

- 1

I started by showing them how to calculate the electric field generated by a single infinite plane whit homogeneous charge distribution. The field is [itex] E_0={\sigma \over 2 \epsilon_0} [/itex]. The first question regarded the dependence of this field with this distance. Is it constant at all distances? Also at infinite? I assumed so, since the plane itself is infinite.

Then we moved to the case with two planes with opposite charges distribution. The field in this case would just be [itex] E_0={\sigma \over \epsilon_0} [/itex] and so the capacitance [itex] C={Q \over \Delta V} =\epsilon_0{S \over d} [/itex] where S and d are the surfaces of the plane and the distance between the two. To obtain this result, though, I used the electric field generated by an infinite plane, and then I assumed che charge distribution to be the ratio over the total charge and the surface. What did I miss in the passage from an infinite plane to a finite one? Is the electric field generated by a finite plane equal to the one generated by an infinite one? If so how does one answer to the first question?

The last part regarded spherical capacitors. To calculate its capacitance one in general uses only the electric field due to the charge present in the inner capacitor? Why is there no contribution from the opposite charge present in the external one?

Thanks for the help!